Recently, a transparent organic polymer material has been used as a transparent material in place of an inorganic glass. When these materials have been used, for example, as an optical resin, there has generally been demanded an optical resin having required general properties such as transparency, thermal properties and mechanical properties, while attaining a high refractive index.
A technique concerning such a resin has been disclosed in Patent Document 1. In the Document, a thietane compound containing a metal has been disclosed. Further, an optical resin having high refractive index exceeding a refractive index (nd) of 1.7 has been disclosed.    [Patent Document 1] International Publication Pamphlet No. 2005/095490    [Patent Document 2] Japanese Unexamined Patent Application publication No. 2003-327583